Opis

When did life first appear on Earth and what form did it take? This practical guide brings together materials that have been claimed to comprise the earliest fossil record. It is suitable for an astrobiologist and astronaut.Acknowledgments Setting the scene, an introduction by Martin Brasier Milestones in the search for early life on Earth The Eozoon debate and the 'Foraminosphere' The Cyanosphere, phase 1 The Cyanosphere, phase 2 Implications Recommended reading PART A: Investigating life in early Archean rocks 1. What can we expect to find in the earliest rock record? Introduction 1.1. Body fossils 1.2. Trace fossils 1.3. Chemical fossils 2. The difficulties of decoding early life Introduction 2.1. Non-biological artefacts 2.2. Post-depositional contamination 2.3. The pros and cons of the 'Principle of Uniformity' 2.4. A benchmark for microfossils and stromatolites 3. Establishing the criteria for early life on Earth Introduction 3.1. Antiquity criteria 3.1.1. General antiquity criteria 3.1.2. Additional antiquity criteria specific to microfossils 3.1.3. Additional antiquity criteria specific to trace fossils 3.2. Biogenicity criteria 3.2.1. General biogenicity criteria 3.2.2. Additional biogenicity criteria specific to microfossils 3.2.3. Additional biogenicity criteria specific to trace fossils 3.3. The problem of stromatolites 4. Fulfilling the criteria for early life on Earth Introduction 4.1. Where to look? -- Archean cratons 4.1.1. Geology of the Pilbara craton 4.1.2. Geology of the Barberton greenstone belt, Kaapvaal craton 4.1.3. Geology of southwest Greenland 4.2. Typical rocks found in the early Archean that could host life 4.2.1. Chert 4.2.2. Pillow basalt 4.2.3. Sandstone 4.2.4. Hydrothermal deposits 5. Techniques for investigating early life on Earth Introduction 5.1. Geological mapping 5.2. Radiometric dating 5.3. Optical microscopy 5.4. Scanning electron microscopy (SEM) 5.5. Transmission electron microscopy (TEM) 5.6. Secondary ion mass spectrometry (SIMS and NanoSIMS) 5.7. Laser-Raman micro-spectroscopy 5.8. Near edge x-ray absorption fine structure spectroscopy (NEXAFS) and electron energy loss spectrometry (EELS) 5.9. Synchrotron x-ray tomography 5.10. Atomic force microscopy (AFM) 5.11. Molecular fossils 5.12. Carbon isotopes 5.13. Sulphur isotopes 5.14. Other isotopic systems Summary of techniques Part B: An atlas of claims for early Archean life Introduction 1. >3700 Ma, Isua Supracrustal Belt and Akilia Island, S.W. Greenland 2. ~3490 Ma, Dresser Formation, East Pilbara, Western Australia Summary of claims for early life from this Formation 3. ~3470 Ma, Mount Ada Basalt, East Pilbara, Western Australia 4. ~3460 Ma, Apex Basalt, East Pilbara, Western Australia 5. ~3450 Ma, Hoogenoeg Formation, Barberton, South Africa 6. ~3450 Ma, Panorama Formation, East Pilbara, Western Australia 7. ~3400 Ma, Strelley Pool Formation, East Pilbara, Western Australia Summary of claims of early life from this Formation 8. ~3416-3334 Ma, Kromberg Formation, Barberton, South Africa 9. ~3350 Ma, Euro Basalt, East Pilbara, Western Australia 10. ~3250 Ma, Fig Tree Group, Barberton, South Africa 11. ~3240 Ma, Kangaroo Caves Fm., East Pilbara, Western Australia 12. ~3200 Ma, Moodies Group, Barberton, South Africa 13. ~3200 Ma, Dixon Island Formation, West Pilbara, Western Australia 14. ~3000 Ma, Cleaverville Formation, West Pilbara, Western Australia 15. ~3000 Ma, Farrel Quartzite, East Pilbara, Western Australia 16. The Imposters. Younger biological contaminants and non-biological artefacts Index